It unsubs and reports spam.

If it's a spammer, then unsubscribing just lets them add your email address to a list of known-active email addresses, which they can sell for more money to other scammers.

If you subscribed to something, then unsubscribe, sure. If you didn't subscribe (AND accept a confirmation right after), then mark as spam ONLY - don't unsubscribe also.

If someone else successfully subscribed you to something (accidentally or on purpose), then there wasn't a confirmation process - these people should be marked as spam.